D-Link DI-707P - Manual (Page 8)

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Point -to-Point Tunneling Protocol (PPTP)
PPTP uses proprietary means of connecting two private networks over the Internet.
PPTP is a way of securing the information that is communicated between
networks. PPTP secures information by encrypting the data inside of a packet
.
IP Security (IPSec)
IPSec provides a more secure network-to-network connection across the Internet
or a Wide Area Network (WAN). IPSec encrypts all communication between the
client and server whereas PPTP only encrypts the data packets.
Both of these VPN implementations are used because there is not a standard for
VPN server software. Because of this, each ISP or business can implement its
own VPN network making interoperability a challenge.